1. Field of the Invention
This invention relates generally to blood transfusions or reinfusions and more particularly to a method of removing undesirable elements from whole blood once it has been removed from a patient and prior to its being reinfused or transfused.
2. Description of the Prior Art
Whole human blood includes at least three types of specialized cells. These are the red blood cells, white blood cells and platelets. All of these cells are suspended in plasma, a complex aqueous solution of proteins and other chemicals.
When removing blood from a donor for homologous transfusion, for reinfusion or when obtaining blood for plasmapheresis, and/or salvaging blood from a body cavity or wound site, it is important to remove the undesirable elements from the blood before reinfusing or transfusing the blood into a patient. The undesirable elements that must be removed include plasma, activated clotting factors and/or byproducts of coagulation, drugs, cellular debris, platelets and leukocytes, otherwise referred to as white blood cells. The only element of the blood which remains after the removal of the undesirable elements are the red blood cells, which are the desired element for reinfusion or transfusion.
Numerous systems have been developed for cleaning whole blood by removing the undesirable elements, an example of which is disclosed in U.S. Pat. No. 4,086,924 issued to Latham, Jr. These systems include means for removing the blood from a patient, adding an anticoagulant to the blood, separating the various components of the blood usually in a centrifugal separator, washing the desirable red blood cell component which is retained in the separator with a saline solution, and then reinfusing the clean red blood cells into the patient from whom the blood was drawn or transfusing the blood into a donor patient.
The separation and washing process, as mentioned above, is normally accomplished in a centrifugal separator wherein the whole blood, including the anticoagulant, is introduced through a central column of a rotating bowl so that the blood will flow to the outer edge of the bowl and subsequently upwardly along a circumferential wall of the bowl until the lighter elements are discharged through an outlet provided near the top of the bowl. The red blood cells being the heaviest component of whole blood remain in the bowl for the longest period of time so that the lighter undesirable elements are discharged before the red blood cells fill the separating bowl. Once the bowl is substantially full of red blood cells, the cells have become compacted against the circumferential wall of the bowl and portions of the plasma remain trapped in the interstitial spaces between the red blood cells. In order to remove the plasma from the spaces between the red blood cells, it has been common practice to pass a saline solution through the centrifugal separator to wash the plasma out of the interstitial spaces between the cells.
One problem with this prior art system of washing the red blood cells with a constant flowing saline solution is that the flow rate necessary to rapidly wash the red blood cells is also sufficient to carry the red blood cells through the outlet at the top of the bowl thereby washing valuable blood cells out of the separator making the system inefficient. On the other hand, if a constant flow rate of saline passing through the separator is not great enough to agitate the blood cells, it will not adequately clean the cells as it will not flush the plasma out of the spaces between the red blood cells in a short period of time. In other words, the red blood cells being compacted by the centrifugal forces of the separator bowl require a relatively high flow rate of saline to separate the blood cells so that the plasma and other undesirable elements can be removed, but this relatively high flow rate is detrimental in that it carries valuable red blood cells out of the separator bowl.
It is accordingly a primary object of the present invention to provide a new and improved method of cleaning red blood cells which is more efficient and does not result in a significant loss of red blood cells.
It is another object of the present invention to provide a method of cleaning red blood cells which utilizes a greater volume of wash solution in a given period of time so as to more thoroughly clean the red blood cells without a significant loss thereof.